The long term objective of this project is to understand the topography of the mammalian sperm surface and how the sperm surface interacts with the egg during fertilization. The mechanisms that restrict individual surface antigens to localized domains on the sperm surface will be investigated. Surface antigens that are localized may be maintained in their domains by diffusion barriers at the domain boundary, by being immobilized, or by other mechanisms. We have previously postulated that the freely diffusing sperm surface antigen, PT-1, is maintained in its domain by a membrane barrier to protein diffusion. The nature of this membrane barrier will be investigated. Proposed experiments will identify other freely diffusing or immobilized antigens by fluorescence redistribution after photobleaching (FRAP). If localized surface antigens that are immobilized are found, we will test the hypothesis that they are attached to an "immobilization network" and identify and characterize this network by purifying it. The discovery that two antigens migrate from their initial domain to a new domain during capacitation and immediately after the acrosome reaction will be followed up by experiments to define the mechanism and functional significance of these migrations. It will be tested if the PT-1 antigen migration is required for capacitation. The hypothesis will be evaluated that the PH-20 antigen, which migrates after the acrosome reaction, has a required function in sperm-zona pellucida binding. The monoclonal antibody PH-30 specifically inhibits sperm-egg plasma membrane fusion. The purified PH-30 antigen and other purified antigens recognized by antibodies found to block sperm-egg fusion will be tested for their activities in fusion with zona-free eggs. These investigations have a two-fold purpose. Development of new approaches to both contraception and to the treatment of infertility can be advanced by a better understanding of sperm surface topography and sperm-egg interaction.